A mobile communication system has been developed based on the wireless communication network for the purpose of providing communication services while ensuring the user's mobility. The mobile communication system provides high-speed data communication services in addition to voice call services.
For example, the mobile communication system has evolved from a 3rd Generation Partnership Project (3GPP) system into a Long Term Evolution (LTE) system. The LTE system provides data communication services at a maximum of about 100 Mbps.
The LTE system has evolved into an LTE-Advanced (LTE-A) system for the purpose of improving the transmission rate. In the following description, for convenience, the LTE system and the LTE-A system will both be referred to as an ‘LTE system’.
The LTE system may provide voice call services for a User Equipment (UE) both in a Packet Switched (PS) domain and a Circuit Switched (CS) domain. For example, Voice over LTE (VoLTE) technology is technology in which the LTE system supports voice call services in the PS domain, and Circuit Switched FallBack (CSFB) technology is technology in which the LTE system supports voice call services in the CS domain. The VoLTE technology may be used as the same concept as Voice over IP Multimedia Subsystem (IMS) (VoIMS) in the LTE system.
In the LTE system, a UE performs a CSFB procedure upon request for an incoming or outgoing voice call service while using the LTE network. The CSFB procedure defines an operation of switching from the LTE network (or the PS network) to the 3G network (or the CS network).
For example, if an incoming call for a UE occurs in the LTE system, a base station or an Evolved Node B (ENB) notifies the UE of the call termination in accordance with a predefined paging procedure. Upon recognizing the call termination, the UE sends a service request message to the eNB in response thereto. The service request message sent by the EU enables the CSFB procedure to be conducted in the LTE system. In the CSFB procedure, it is premised that a UE cannot use the LTE network and the 3G network at the same time.
However, the LTE system does not provide a scheme for handling paging for a CS service while a paging procedure by a PS service is ongoing, for a UE in an idle mode.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.